1. Field of the Invention
The present invention relates to a seat reclining mechanism.
2. Description of the Related Art
Heretofore, there has been known a seat reclining mechanism designed to be mounted to a seat cushion and a seat back so as to allow the seat back to be reclined. JP 2001-17259A and JP 2004-154585A disclose a reclining mechanism which comprises a guide bracket adapted to be mounted to either one of a seat cushion and a seat back, an internal gear member (i.e., internally-toothed gear member) adapted to be mounted to a remaining one of the seat cushion and the seat back, a plurality of lock gear members disposed between the guide bracket and the internal gear member and adapted to be slidingly guided in a radial direction, a rotatable cam adapted to move the lock gear members in both a lock direction causing the lock gear members to be brought into engagement with the internal gear member and an unlock direction causing the lock gear members to be released from the engagement with the internal gear member, and a lock spring biasing the rotatable cam in a lock-causing rotation direction.
In this mechanism, when an operator operates an operation lever to rotate the rotatable cam in a direction opposite to the lock-causing rotation direction, the lock gear members are moved in the unlock direction through a circular lever (actuating plate), and released from the engagement with the internal gear member. Thus, the seat back can be forwardly or rearwardly inclined. Then, when the operator releases his/her hand from the operation lever, the rotatable cam is rotated in the lock-causing rotation direction by a biasing force of the lock spring, and the lock gear members are moved in the lock direction and brought into engagement with the internal gear member. Thus, the seat back is locked at an intended inclined position.
In some types of vehicles, a reclining mechanism is designed to allow a seat back, for example, of a rear seat, to have a horizontal posture when it is moved to a forwardmost inclined position, so as to expand a luggage space. In this case, the reclining mechanism includes one type adapted to lock the seat back at the forwardmost inclined position, and another type adapted to keep the seat back from being locked at the forwardmost inclined position.
For example, the reclining mechanism disclosed in the JP 2001-017259A is designed as the type adapted to keep the seat back from being locked at the forwardmost inclined position. Specifically, the internal gear member (i.e., internally-toothed gear member) is formed with a free-zone arc portion (narrow guide groove), and one of the lock gear members (lock plates) is formed with a protrusion (second guidable piece). In this reclining mechanism, when the seat back is moved to the forwardmost inclined position, the protrusion is brought into contact with the free-zone arc portion, so that the seat back is kept from being locked at the forwardmost inclined position.
Depending on a vehicle type, it is desired sometimes to set up the two types of reclining mechanisms: one adapted to keep a seat back from being locked at a forwardmost inclined position when the seat back is moved to the forwardmost inclined position; and the other adapted to lock the seat back at the forwardmost inclined position. In this case, plural types of internal gear members have to be prepared for one vehicle type, which leads to a problem about an increase in cost.